1. Field of the Invention
The present invention relates generally to a three-wheel vehicle, more particularly, to a concentric intermediate sprocket assembly for a three-wheel vehicle.
2. Description of Related Art
The three-wheel vehicle of the present invention is significantly improved over the straddle-type three-wheel vehicles with two front wheels and one rear wheel that are found in the prior art.
U.S. Pat. No. 4,787,470 discloses a three-wheel vehicle with two front wheels and a single rear wheel having a body formed by an ATV (all terrain vehicle) frame carrying two front fenders, one rear fender, and a straddle-type seat. An engine is supported on the frame but is exposed to the exterior of the vehicle body. The 470 patent also discloses a vehicle with a trailing arm assembly that rotatably supports the rear wheel for suspension movement relative to the frame. The trailing arm includes a pair of arm portions that extend on opposite sides of the rear wheel. The arm portions are joined to a single forwardly extending arm portion that is pivotally supported on the frame about a pivot axis. In addition, the 470 patent also discloses a sprocket supported by the trailing arm assembly at a point between the pivot axis and the end of the trailing arm assembly. The sprocket is supported on an intermediate shaft and engages a first endless chain driven by an output shaft of the engine. The intermediate shaft includes another sprocket on an outer end that engages and drives a second endless chain that drives the rear wheel. An output shaft of the engine drives the second endless chain that is connected between the output shaft and the intermediate shaft. As the intermediate shaft is on the trailing arm and the output shaft is on the frame, the lengths of the endless chains will vary as the trailing arm is displaced relative to the frame.
U.S. Patent Application Publication 2002/0017765 A1 discloses a three-wheel vehicle, including two front wheels and a single rear wheel, based on a snowmobile frame. The rear wheel is driven by an endless drive chain that extends between a sprocket on the rear wheel and a sprocket connected to a drive shaft. The drive shaft sprocket is connected to a continuously variable transmission (CVT) of an internal combustion engine by a endless chain.
Prior art three-wheel vehicles, such as the one described in the 470 patent, suffer from a number of shortcomings. For example, transmitting power from the engine to the rear wheel on vehicles, especially those that rely on a chain drive, poses particular difficulties. Specifically, if the drive chain is connected between the output shaft of the engine and the rear drive wheel and the distance from the engine output shaft to the drive wheel is particularly long, as the rear suspension flexes under stress, the chain length varies. This may cause difficulties, especially if the rear suspension collapses due to a significant extent. In particular, if the rear swing arm collapses toward the frame a sufficient distance, the chain tension may become sufficiently relaxed (i.e., slack) that the chain may disengage from the sprocket attached to the engine output shaft or the sprocket attached to the axle on which the rear wheel is disposed. Alternatively, if the rear swing arm extends a sufficient distance from the frame, a sufficient amount of tension may be applied to the chain to cause it to break.
As another example, the position of the drive shaft and the drive shaft sprocket of the 765 application publication is not adjustable and slack or tension that develops in the chain between the rear wheel sprocket and the drive shaft sprocket or in the chain between the drive shaft sprocket and the CVT may not be compensated for.
A CVT is considered to be superior to a traditional geared transmission because, unlike a traditional gear box that provides four or five separate gears, a CVT provides an infinite number of “gears.” As a result, CVT's are much more efficient at transmitting torque from the engine to the driven wheel.
Although the three-wheel vehicle disclosed in the 765 application publication includes a CVT, as the vehicle is based on a snowmobile frame, the output shaft of the CVT is placed above the drive shaft of the engine for connection to the endless track propulsion system of the snowmobile. Upon conversion of the snowmobile to the three-wheel vehicle, the output shaft of the CVT is connected to the drive shaft sprocket through a chain, which decreases the efficiency of the CVT to drive the rear wheel of the three wheeled vehicle.
The difficulties associated with chain drives for vehicles, especially three-wheel vehicles, has created a need for an improved construction where the chain driving the rear wheel is not subjected to excessive tension or slack and is driven with the highest possible efficiency by the engine.